Electronic systems can often be implemented in a micro-electronic circuit that is typically referred to as an IC or integrated circuit. These electronic systems typically include a number of passive and active electronic components, including but not limited to: resistors, capacitors, inductors, logic gates, linear amplifiers, voltage regulators, signal processors and converters, to name a few.
Integrated circuits are typically created on a single silicon wafer, where the silicon is processed through deposition, doping, etching, and other semiconductor processes to create the various electrical characteristics that make the circuit functions. Since the integrated circuit is typically made from a single substrate, there are limited number of materials (e.g., metal, poly-silicon, dielectric, doped silicon, etc.) that are available to make the various electrical components. As a consequence of the limited materials available, it is often the case that the “chip” or IC solution of the original system concept cannot be realized using the same types of passive components (resistors, capacitors, inductors, etc) as the system design. In short, it is physically impossible to create certain varieties of electrical components on an integrated circuit in the same manner as their discrete circuit equivalents. However, creative integrated circuit designers have found that various integrated circuit materials such as diffusion and poly-silicon can be used to create passive components such as resistors and capacitors.
Although it is possible to create passive components on an integrated circuit, many of these passive components exhibit characteristics that simply did not exist for their passive component equivalents. For example, a resistor in an integrated circuit may have capacitive characteristics that simply did not exist in a discrete resistor. Moreover, due to limitations in integrated circuit processes, it is impracticable to use high precision passive components (e.g., resistors accurate to 1% of their designed value) in an integrated circuit, where resistance values can typically vary by 20% or more from their nominal value.
Integrated circuit designers have developed a variety of ways to adjust resistor values on an integrated circuit such that improved circuit performance can be achieved. In one example, fuse and/or anti-fuse technologies have been used to allow an adjustment to the nominal resistance of a particular component in the circuit. In another example, a thin film layer has been deposited on the surface of the integrated circuit that includes high precision resistors that can be adjusted by a laser beam trimming system. In other examples, circuit designers have changed the overall circuit topology such that the high-precision resistor values are not required in the system on a chip (SOC) implementation.